What is a “Planet”?

What exactly is the definition of a planet? Is Pluto a planet because of tradition, or should it technically not be considered a planet? This SF Chronicle article looks at the definition of what a planet is, and a proposed solution a University of California astronomer has. Brown and his colleagues are on a constant hunt for large objects in Pluto’s neighborhood, and three years ago they found one 4 billion miles away. They named it Quaoar (pronounced Kwah-wahr) and called it a KBO. Last year, they discovered an even stranger object orbiting the sun 8 billion miles away, far more distant than Pluto. They named it Sedna, and Brown called it a “planetoid,” but not a planet.